In-situ infrared spectroscopy of organic electrochemical devices

Organic electrochemical transistors (OECTs) offer low voltage operation and a feasible platform for flexible, large-area, and low-cost devices, especially in the context of printed electronics. However, these devices often suffer from sluggish performance as a result of ion intercalation into the bulk of the organic semiconductor. We have characterized the time dependent behaviour of OECTs based on poly(3-hexylthiophene) (P3HT) and a poly(ethylene oxide): lithium perchlorate (PEO:LiClO4) gate dielectric using in-situ infrared spectroscopy. Because charge carriers in P3HT have a characteristic absorption in the mid infrared, we can monitor the rate of device charging and discharging spectroscopically. The dependence of the charging rate on parameters such as channel length, semiconducting polymer thickness and dielectric thickness have been investigated. Our results indicate that several distinct mechanisms are at play, with the rate limiting step being determined by device geometry. Using these results, we have also examined the effect of the structure of the counter-ion on its diffusivity in the organic semiconductor once doping occurs.